# Input math problem

1. Dec 26, 2005

### asdf1

y +y`+y=r(t)
why's r(t) the input and not t?

2. Dec 26, 2005

### marlon

Because the right hand side of that equation denotes a function of t.

r(t) could be t but it can also be every other function that depends on t.

Basically, r(t) is the most general form to denote "a function of t"

marlon

3. Dec 26, 2005

### HallsofIvy

Staff Emeritus
That's not really mathematics- it's "Engineer speak".

From the point of view of an Engineer, a differential equation is a machine to which you supply an "input" and get an "output". The differential operator y"+ y'+ y is the machine. Whatever function you have on the right hand side is the "input" (which varies with t) and y(t) satisfying the equation is the "output".

(Edited- thanks, Marlon.)

Last edited: Dec 27, 2005
4. Dec 26, 2005

### marlon

The differential operator is not y''+y' but y''+y'+y

marlon

5. Dec 28, 2005

### asdf1

thank you very much!!!